Trench formation using rounded hard mask

ABSTRACT

A method embodiment includes forming a hard mask over a dielectric layer, patterning the hard mask to form an opening, forming a passivation layer on sidewalls of the opening, and forming a trench in the dielectric layer by extending the opening into the dielectric layer using an etching process. The sidewalls of the opening are etched to form a rounded profile in the hard mask and a substantially perpendicular profile in the dielectric layer.

TECHNICAL FIELD

The present invention relates generally to a system and method forsemiconductor device manufacturing, and, in particular embodiments, to asystem and method for creating trenches in a semiconductor device layer.

BACKGROUND

Generally, a semiconductor device includes interconnect structureselectrically connecting active devices (e.g., transistors or capacitors)to create functional circuits. These interconnect structures includeconductive features (e.g., metal lines and vias) formed in variousdielectric layers. The formation of conductive features (e.g., metallines and vias) in a dielectric layer generally involves patterning thedielectric layer to form trenches and filling the trenches with aconductive material.

Typically, trench formation is done using a combination ofphotolithography and etching. A hard mask may be disposed over adielectric layer as a patterning mask for etching the dielectric layer.As the desired critical dimensions (e.g., width of trenches and/or thespacing between trenches) become smaller and smaller in advancedsemiconductor devices, traditional methods for patterning hard masks anddielectric layers may result in large overhangs on sidewalls of a trenchand other issues. These defects may negatively affect yield, subsequenttrench filling processes, and leakage control issues.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1-8 are cross-sectional views of various stages of manufacturingfor forming trenches in a semiconductor device in accordance withvarious embodiments; and

FIG. 9 illustrates a flow chart for forming trenches in a semiconductordevice layer in accordance with various embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable concepts that can be embodied in a wide varietyof specific contexts. The specific embodiments discussed areillustrative, and do not limit the scope of the disclosure.

Trench formation in semiconductor devices using rounded hard masks isprovided in accordance with various embodiments. The intermediate stagesof forming the trenches in the semiconductor device are illustrated. Thevariations of the embodiments are discussed. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements.

FIG. 1 shows a portion of a semiconductor device 100. Semiconductordevice 100 includes a dielectric layer 102, which may be disposed over asubstrate (not shown). Active devices (not shown) such as transistorsmay be formed at a top surface of the substrate. The substrate may be abulk silicon substrate although other semiconductor materials includinggroup III, group IV, and group V elements may also be used.Alternatively, the substrate may be a silicon-on-insulator (SOI)substrate.

Dielectric layer 102 may be an inter-layer dielectric (ILD) or aninter-metal dielectric layer (IMD) formed using any suitable method(e.g., chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), aspin on technique or the like). Dielectric layer 102 may be formed oflow-k dielectric materials having k values, for example, lower thanabout 4.0. Dielectric layer 102 may also formed of extra low-k (ELK)material having a k-value lower than about 2.8. In some embodiments,dielectric layer 102 may comprise silicon oxide, SiCOH, or the like.Although FIG. 1 illustrates only one dielectric layer 102, semiconductordevice 100 may include numerous dielectric layers. An etch stop layer108 (e.g., a silicon nitride layer, a silicon carbide layer, or thelike) may be formed under dielectric layer 102.

An oxide layer 104 and a hard mask 106 may be formed over dielectriclayer 102. Hard mask 106 may be a metal hard mask comprising, forexample titanium nitride, titanium oxide, tantalum nitride, or the like.Other hard mask materials may also be used. Hard mask 106 may furtherinclude an anti-reflective coating layer (e.g., a nitrogen freeanti-reflective coating (NFARC), not shown) to aid in the patterning ofhard mask 106. Oxide layer 104 may be disposed between hard mask 106 anddielectric layer 102, and oxide layer 104 may be formed, for example,through thermal oxidation of dielectric layer 102. Oxide layer 104 mayact as a buffer layer and/or an adhesion layer between dielectric layer102 and hard mask 106. Oxide layer 104 may also act as an etch stoplayer for patterning hard mask 106.

FIG. 2 illustrates the patterning of hard mask 106 to form openings 110.Openings 110 may extend through hard mask 106 and partially into oxidelayer 104. In various embodiments, the patterning of hard mask 106 maybe through a combination of photolithography and etching techniques. Forexample, a photoresist (not shown) may be disposed over hard mask 106.Portions of the photoresist may be exposed (e.g., using an ultravioletlight or an excise laser) through a patterning mask. The exposed orunexposed portion of photoresist may be then removed depending onwhether a positive/negative resist was used, and hard mask 106 may beetched using the patterned photoresist as a mask. Subsequently, thephotoresist may be removed (e.g., using an ashing technique). Theetching of hard mask 106 may include a dry etching process using, forexample, C_(x)F_(y) (i.e., a fluorocarbon such as tetrafluoromethane,octafluoropropane, or the like), N₂, O₂, Ar, or the like as a processgas. Oxide layer 104 may act as an etch stop layer during the patterningof hard mask 106.

FIG. 3 shows the etching oxide layer 104 using hard mask 106 as apatterning mask. The etching extends openings 110 through oxide layer104 and may further extend openings 110 past a top surface of dielectriclayer 102. The etching of oxide layer 104 may also taper sidewalls 110 aof openings 110 to have a slanted, non-perpendicular profile. Forexample, sidewalls 110 a may have an angle of about 80° after etching.

Furthermore, a residual byproduct of the process gas used during theetching process may form a polymer rich passivation layer 112 on exposedsurfaces of semiconductor device 100 (e.g., sidewalls of openings 110).Due to differences in the chemical reaction between the process gas andthe material of hard mask 106 (e.g., a metal) versus oxide layer104/dielectric layer 102, passivation layer 112 may be formed moreprevalently (i.e., thicker) on hard mask 106 than on other surfaces ofopenings 110. As a result of passivation layer 112, the etch rate ofhard mask 106 may be significantly lower than the etch rate of oxidelayer 104 and dielectric layer 102 during subsequent etching processes.The difference in etching rates of hard mask 106 and oxide layer104/dielectric layer 102 allows for improved rounding process control ofmetal layer 106 as will be explained in greater detail below.

The tapering of sidewalls 110 a and the formation of passivation layer112 may be achieved by controlling the process conditions of the etchingprocess used on oxide layer 104, which maybe a dry etch process. Forexample, a larger amount of bias power may be applied to high radiofrequencies during the dry etching than power applied to low radiofrequencies to promote sidewall tapering and passivation layer 112formation in openings 110. In some embodiments, a bias power of about100 W to about 500 W is applied to high radio frequencies while a biaspower of about 0 W to about 50 W is applied to low radio frequencies.Furthermore, the etching process may occur at a pressure of about 20mTorr to about 80 mTorr and at a temperature of about 40° to about 70°Celsius while applying a DC power supply voltage between about 0V andabout negative 500V. Suitable process gases for the formation of apassivation layer may include fluorocarbon gases (e.g., C_(x)F_(y),applied at a flow rate of about 20 standard cubic centimeters per minute(sccm) to about 50 sccm), N₂ (e.g., at a flow rate of about 0 sccm toabout 100 sccm), O₂ (e.g., at a flow rate of about 0 sccm to about 25sccm), Ar (e.g., at a flow rate of about 0 sccm to about 100 sccm), orthe like. A byproduct of the process gas used during etching forms apassivation layer 112 on sidewalls of openings 110.

FIG. 4 illustrates the further etching of dielectric layer 102 to extendopenings 110 into dielectric layer 102, forming trenches. The etchingprocess used on dielectric layer 102 may further cause sidewalls 110 dof openings 110 in hard mask 106 to have a rounded profile. The roundedprofile allows for increased process robustness, for example, byreducing overhang formation, or the like.

As previously discussed, the formation of passivation layer 112 reducesthe etch rate of hard mask 106 passivated by the polymer rich layer(e.g., sidewall 110 d). The etch rate of hard mask 106 may besufficiently lower than the etch rate of oxide layer 104, and the etchrate of oxide layer 104 and dielectric layer 102 to allow for therounding of hard mask 106 during etching while still achievingsubstantially perpendicular profiles for sidewalls (e.g., sidewalls 110b and 110 c) of openings 110 in oxide layer 104 and dielectric layer102. Because passivation layer 112 is also formed on sidewalls ofopenings 110 in oxide layer 104, the etch rate of oxide layer may alsobe lower than the etch rate of dielectric layer 102. For example, theetch rate of dielectric layer 102 may be between about 10 Å/s and about20 Å/s, the etch rate of oxide layer 104 may be between about 5 Å/s andabout 10 Å/s, while the etch rate of hard mask 106 may be less than 1Å/s. These differences in etch rates allows for better control duringthe rounding process and facilitates accuracy in achieving desiredcritical dimensions for semiconductor device while forming trenches indielectric layer 102 (e.g., width W1 of the trench opening and width W2of the isolation spacing between trenches).

In some embodiments, after the etching process shown in FIG. 4,sidewalls 110 d of openings 110 in hard mask 106 may have a slope anglebetween about 70° to about 80°, whereas sidewalls 110 c/110 b ofopenings 110 in oxide layer 104 and dielectric layer 102 may have aslope with an angle greater than about 85°. As a result of thesubstantially perpendicular profile of sidewall portions 110 c and 110b, more desirable critical dimensions for semiconductor device 100 maybe achieved during trench formation while simultaneously rounding hardmask 106. For example, the process described generally allows for asmaller width W1 of trench openings. The process may also allow for anincreased width W2 of spacing between trenches for improved isolationbetween trenches without increasing the pitch (i.e., W1 plus W2) oftrenches 110. Thus, a wider process window for trench-fill and betterleakage control may be achieved in semiconductor device 100.

To promote rounding of hard mask 106, a larger bias power may be appliedto high radio frequencies during etching than low radio frequencies topromote hard mask 106 rounding. However, sufficient bias power may beapplied to low radio frequencies to provide a desired bombardment powerfor etching trenches. In some embodiments, a bias power of about 50 W toabout 200 W is applied to high radio frequencies while a bias power ofabout 0 W to about 100 W is applied to low radio frequencies.Furthermore, the etching process may occur at a pressure of about 20mTorr to about 80 mTorr and at a temperature of about 50° to about 70°Celsius. Suitable process gases for the formation of a passivation layermay include fluorocarbon gases (e.g., C_(x)F_(y), applied at a flow rateof about 20 sccm to about 50 sccm), N₂ (e.g., at a flow rate of about 0sccm to about 100 sccm), O₂ (e.g., at a flow rate of about 0 sccm toabout 25 sccm), Ar (e.g., at a flow rate of about 0 sccm to about 100sccm), or the like.

Subsequently, in FIG. 5, a planarization (e.g., a chemical mechanicalpolish (CMP) or an etch back technique) may be applied to remove hardmask 106 and oxide layer 104. Thus, trenches 110 having substantiallyperpendicular sidewalls (e.g., having an angle greater than 85°) areformed in dielectric layer 102. Trenches 110 may have a width W1 and beseparated from other trenches by a width W2. W1 and W2 may varydepending on desired critical dimensions of semiconductor device 100. Insome embodiments, width W1 maybe between about 44 nm and about 64 nm,and width W2 may be between about 20 nm and about 26 nm.

FIG. 6 illustrates the formation of a barrier layer 114 in trenches 110.Barrier layer 114 may cover sidewalls and a bottom surface of trenches110. Barrier layer 114 may comprise, for example, titanium nitride,titanium oxide, tantalum nitride, tantalum oxide or the like. Barrierlayer 114 may prevent the diffusion of metallic material of subsequentlyformed vias into the surrounding dielectric layer 102. Barrier layer 114may be deposited using any suitable deposition process, such as CVD,PVD, a conformal deposition process, or the like.

FIGS. 7 and 8 illustrate the filling of trenches 110 to form conductivefeatures 116 (e.g., lines or vias) in dielectric layer 104. First, asillustrated by FIG. 7, a metallic material 116 such as copper, a copperalloy, tungsten, aluminum, or another suitable conductor may bedeposited into trenches 110. The deposition of metallic material 116 mayoverflow trenches 110 and dielectric layer 102. Subsequently, asillustrated by FIG. 8, a planarization (e.g., CMP or etch back) maybeused to remove overflow portions. As part of the planarization, topportions of barrier layer 114 may also be removed. Thus, conductivefeatures 116 are formed in dielectric layer 102.

FIG. 9 illustrates a process flow 200 for forming trenches/conductivefeatures in a dielectric layer in accordance with various embodiments. Ahard mask may be disposed over the dielectric layer with an oxide layerdisposed between the hard mask and the dielectric layer. First, in step202, the hard mask disposed is patterned, for example, using acombination of photolithography and etching.

Next in step 204, the oxide layer may be etched to extend the openingsthrough the oxide layer. The etching process conditions applied to theoxide layer may be selected to taper sidewalls of the openings. Forexample, after the etching process, sidewalls of the openings may besloped at an angle of about 80°. A process gas used during the etchingprocess may further form a polymer rich passivation layer on sidewallsof the openings. In particular, the passivation layer may be formed onsidewalls of the openings in the hard mask. The passivation layerreduces the etch rate of the hard mask compared to the etch rate of theoxide layer and the dielectric layer in subsequent process steps.

In step 206, another etching process may then be performed to formtrenches in the dielectric layer by extending the openings into thedielectric layer. The process conditions of this etching process may becontrolled to achieve desired critical dimensions in the dielectriclayer. The sidewalls of the opening may also be etched to form a roundedprofile in the hard mask and a substantially perpendicular profile inthe oxide layer and the dielectric layer. The passivation layer reducesthe etch rate of the hard mask and allows for the etching process toround the hard mask while still forming substantially perpendicularsidewalls for portions of the openings in the oxide and dielectriclayers. The rounded hard mask reduces overhang issues and increases theprocess window for filling the trenches in subsequent steps. In step208, the dielectric layer is exposed by removing the hard mask and oxidelayer, for example, using a planarization process. Finally, in step 210,the openings are filled with a conductive material (e.g., a metal) toform conductive features (e.g., lines and/or vias) in the dielectriclayer.

In accordance with an embodiment, a method includes forming a hard maskover a dielectric layer, patterning the hard mask to form an opening,forming a passivation layer on sidewalls of the opening, and forming atrench in the dielectric layer by extending the opening into thedielectric layer using an etching process. The sidewalls of the openingare etched to form a rounded profile in the hard mask and asubstantially perpendicular profile in the dielectric layer.

In accordance with another embodiment, a method includes forming anoxide layer over a dielectric layer and forming a hard mask over theoxide layer. The method further includes patterning the hard mask toform an opening, etching the oxide layer to taper sidewalls of theopening, and etching the dielectric layer to extend the opening into thedielectric layer. The method further includes etching sidewalls of theopening to form a profile for the sidewalls, and wherein the profile isrounded in the hard mask and substantially perpendicular profile in theoxide layer and the dielectric layer

In accordance with yet another embodiment, a method includes patterninga hard mask to form an opening, wherein the hard mask is disposed over adielectric layer and etching an oxide layer disposed between the hardmask and the dielectric layer. Etching the oxide layer extends theopening through the oxide layer, tapers sidewalls of the opening, andforms a passivation layer on the sidewalls of the opening. The methodfurther includes etching the dielectric layer. Etching the dielectriclayer extends the openings into the dielectric layer, rounds thesidewalls of the opening in the hard mask, and forms substantiallyperpendicular sidewalls of the opening in the oxide layer and dielectriclayer. The dielectric layer is then exposed by removing the hard maskand the oxide layer, and the opening is filled with a metallic materialto form a conductive feature in the dielectric layer

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

1. A method comprising: forming a hard mask over a dielectric layer;patterning the hard mask to form an opening; forming a passivation layeron sidewalls of the opening; forming a trench in the dielectric layer byextending the opening into the dielectric layer using an etchingprocess; and etching the sidewalls of the opening to form a roundedprofile in the hard mask and a substantially perpendicular profile inthe dielectric layer.
 2. The method of claim 1 further comprisingforming an oxide layer between the hard mask and the dielectric layer,wherein forming the passivation layer comprises etching the oxide layerto extend the opening through the oxide layer and using a process gasused in etching the oxide layer to form the passivation layer.
 3. Themethod of claim 2, wherein etching the oxide layer further comprisestapering the sidewalls of the opening.
 4. The method of claim 3, whereintapering the sidewalls of the opening comprises tapering the sidewallsto have a first angle defined by the sidewalls of the opening and a topsurface of the dielectric layer, and wherein the first angle is about80°.
 5. The method of claim 1, wherein the rounded profile has a secondangle defined by the sidewalls of the opening in the hard mask and a topsurface of the dielectric layer, wherein the substantially perpendicularprofile has a third angle defined by the sidewalls of the opening in thedielectric layer and the top surface of the dielectric layer, whereinthe second angle is between about 70° and about 80°, and wherein thethird angle is greater than about 85°.
 6. The method of claim 1 furthercomprising, after forming the trench: exposing the dielectric layer;forming a barrier layer covering sidewalls and a bottom surface of thetrench; and filling the trench with a metallic material.
 7. A methodcomprising: forming an oxide layer over a dielectric layer; forming ahard mask over the oxide layer; patterning the hard mask to form anopening; etching the oxide layer to taper sidewalls of the opening;etching the dielectric layer to extend the opening into the dielectriclayer; and etching the sidewalls of the opening to form a profile forthe sidewalls, wherein the profile is rounded in the hard mask andsubstantially perpendicular in the oxide layer and the dielectric layer.8. The method of claim 7, wherein etching the oxide layer forms apassivation layer on sidewalls of the opening.
 9. The method of claim 7,wherein etching the oxide layer comprises using a fluorocarbon,nitrogen, oxygen, or argon as a process gas.
 10. The method of claim 7,wherein etching the oxide layer comprises applying a first bias power ofbetween about 100 W and about 500 W to high radio frequencies andapplying a second bias power of between about 0 W and about 50 W to lowradio frequencies.
 11. The method of claim 7, wherein etching the oxidelayer comprises etching the oxide layer at a pressure level of betweenabout 20 mTorr and about 80 mTorr.
 12. The method of claim 7, whereinetching the oxide layer comprises etching the oxide layer at atemperature of between about 40° Celsius and about 70° Celsius.
 13. Themethod of claim 7, wherein etching the oxide layer comprises providing asupply voltage of between about 0V and about −500V.
 14. The method ofclaim 7, wherein etching the sidewalls of the opening comprises a firstetch rate for the hard mask, a second etch rate for the oxide layer, anda third etch rate for the dielectric layer, wherein the first etch rateis lower than the second etch rate, and wherein the second etch rate islower than the third etch rate.
 15. The method of claim 14, wherein thefirst etch rate is less than about 1 Å per second, the second etch rateis between about 5 Å per second and 10 Å per second, and wherein thethird etch rate is between about 10 Å per second and 20 Å per second.16. The method of claim 7 further comprising: removing the hard mask andthe oxide layer; forming a barrier layer covering sidewalls and a bottomsurface of the opening; and filling the opening with a metallicmaterial.
 17. The method of claim 7, wherein the hard mask is a metalhard mask.
 18. A method comprising: patterning a hard mask to form anopening, wherein the hard mask is disposed over a dielectric layer;etching an oxide layer disposed between the hard mask and the dielectriclayer, wherein etching the oxide layer extends the opening through theoxide layer, tapers sidewalls of the opening, and forms a polymer richpassivation layer on the sidewalls of the opening; etching thedielectric layer, wherein etching the dielectric layer extends theopenings into the dielectric layer, rounds the sidewalls of the openingin the hard mask, and forms substantially perpendicular sidewalls of theopening in the oxide layer and dielectric layer; exposing the dielectriclayer by removing the hard mask and the oxide layer; and filling theopening with a metallic material to form a conductive feature in thedielectric layer.
 19. The method of claim 18, wherein etching the oxidelayer forms the passivation layer to have a first thickness on surfacesof the hard mask and a second thickness on surfaces of the oxide layer,wherein the first thickness is greater than the second thickness. 20.The method of claim 18, wherein the sidewalls of the opening have afirst angle defined by the sidewalls of the opening and a top surface ofthe dielectric layer of between about 70° and about 80° in the hardmask, and wherein the substantially perpendicular sidewalls have asecond angle defined by the substantially perpendicular sidewalls andthe top surface of the dielectric layer that is greater than about 85°.